Laminated veneer lumber comprising veneer sheets which are obtained by cutting a log into veneer having a thickness of 2-3 mm, by use of a rotary lathe or a slicer, and by then laminating and bonding the same with their grain directions arranged primarily in parallel is widely used as the material of choice for structures and fixtures of a wooden house, e.g., a door, a door frame, a door casing and a door stop. Such lumber is also used for various other items and as a hardwood structural material that combines a decorative material such as a faceplate, a frame and a leg of furniture, a wall trim for ceiling, a skirting, and a base, a faceplate, a door or a counter top of a cupboard.
Laminated veneer lumber (hereinafter LVL) is obtained from logs of broad-leaved trees such as lauans and beech wood, or of acicular trees such as North American woods, Japanese cypress and cedar by chopping the log into longitudinal segments of selected length and turning the segments into veneer sheets of 2-3 mm thickness using a rotary lathe. Veneer sheets thus obtained typically are then dried using a veneer drier, laminated by arranging them in parallel in the grain direction, and bonded with adhesive. The laminated veneer sheets are subjected to a cold press for provisional compression prior to a hot press for heated compression. As is well-known, all woods contain lignin which is a naturally occurring material bonding together adjacent fibers in the wood material. Alternatively, the laminated veneer sheets may be simply subjected to continuous press processing. Subsequently, the lamination of veneer sheets is flattened, cut into a given width and ground on a major surface with a sander to obtain an LVL.
The prior art method of manufacturing LVL is unsatisfactory in that a rotary-cut or sliced veneer sheet is generally wavy rather than flat over its entirety. It is difficult to flatten the veneer sheet obtained by the prior art method even if drying is conducted under pressure, and wavy veneer sheets cannot be firmly bonded with one another when laminated with adhesive.
It is also extremely difficult to obtain a laminated veneer lumber which is generally flat even if the lamination of veneer sheets is subjected to cold and hot presses, or simply to a continuous press processing.